Liquid crystal alignment layers and method of fabrication

ABSTRACT

Methods are provided for making layers with nano-and micro-patterned topographies by laser action or inkjet printing on a first surface. These topographies have a periodicity of 5 nm to 500 μm in a first direction in the plane of the first surface. These layers can be used as anisotropically patterned alignment layers in electro-optical devices and generate an orientational order of at least 0.30.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to alignment surfacetopographies for electro-active devices and more specific to methods offorming these topographies.

2. Background

Electro-optical devices may contain one or more liquid crystal (LC)layers. These layers are comprised of material which undergoes changesin its optical, electrical, and magnetic characteristics under anexternally applied field. These layers are included in toelectro-optical devices because visual changes in these devices occurdue to different orientations of LC molecules during different states ofdevice operation (e.g. completely ON-state, completely OFF-state, andmany other different states in-between). Depending on the operation modeof the electro-optical device, the so-called field-free LC orientation(OFF-state) and a range of predetermined distributions can bedistinguished from the LC orientations under the applied voltage(ON-state). For successful operation and performance of electro-opticaldevices, the LC material should be appropriately aligned during thefield-free state.

BRIEF SUMMARY OF THE INVENTION

In one embodiment, a method is described where a first surface isprovided. A solution is deposited over the first surface via inkjetprinting to form a first anisotropic pattern. The first anisotropicpattern that is formed by the deposition has a first periodicity of 5 nmto 500 μm in a first direction in the plane of the first surface. Thesolution is solidified to form a first anisotropically patternedalignment layer having features with a size of 5 nm to 500 μm.

In one embodiment, the first anisotropic pattern has a secondperiodicity in a second direction in the plane of the surface. In oneembodiment, the first and second directions are different, the first andsecond periodicities are different, and the second periodicity is 5 nmto 500 μm.

In one embodiment, the step of depositing a solution over the firstsurface includes forming a second anisotropic pattern on the firstsurface.

In one embodiment, the step of depositing a solution includes depositingdrops of the solution and the step of solidifying the solution includesa partial coalescence of the drops while retaining at least somestructure of the first periodicity.

In one embodiment, the step of depositing a solution comprises using aninkjet with a nozzle size from 50 nm to 500 μm.

In one embodiment, the first surface is a first surface of a substrate.In one embodiment, the first surface is a first surface of an electrode.In one embodiment, the first surface is a first surface of a separatelayer disposed on an electrode or a substrate.

In one embodiment, the method further comprises providing a firstsubstrate and providing a first electrode disposed over the firstsubstrate. The first surface is disposed over the first electrode. Themethod farther comprises providing a liquid crystal layer disposed overthe first surface, providing a second surface disposed over the liquidcrystal layer, providing a second electrode disposed over the secondsurface, and providing a second substrate disposed over the secondelectrode.

In one embodiment, the step of providing a second surface includesdepositing a solution over the second surface via inkjet printing toform a second anisotropic patterr and solidifying the solution to form asecond anisotropically patterned alignment layer having features with asize of 5 nm to 500 μm. The second anisotropic pattern formed by thedeposition has a third periodicity of 5 nm to 500 μm in a thirddirection in the plane of the second surface.

In one embodiment, the second anisotropic pattern has a fourthperiodicity in a fourth direction in the plane of the second surface.The third and fourth directions are different, the third and fourthperiodicities are different, and the fourth periodicity is 5 nm to 500μm.

In one embodiment, depositing a solution on the first surface compriseseither translational movement of the inkjet over the first surface inthe first direction or translational movement of the substrate in thefirst direction.

In one embodiment, the step of solidifying the solution includesshrinking the solution through ultra-violet irradiation. In oneembodiment, the step of solidifying the solution includes shrinking thesolution through infra-red heating.

In one embodiment, the solution comprises one of or a combination ofconjugated polymers, acrylates, urethanes, organosilanes, and epoxies.In one embodiment, the solution comprises surfactants or binders. In oneembodiment, the solution comprises a solvent comprising one or acombination of alcohols, ketones, aldehydes, alkanes, alkenes, orchlorinated solvents. In one embodiment, the solution comprisesnanoparticles of metals or metal oxides. In one embodiment, the solutioncomprises carbon nanotubes.

In one embodiment, the anisotropically patterned alignment layer iscapable of generating noticeable alignment in a nematic, cholesteric,smectic, discotic, or blue-phase liquid crystal layer.

In one embodiment, the anisotropically patterned alignment layer iscapable of generating alignment with an orientational order parameter ofat least S=0.50 in a nematic liquid crystal layer.

In one embodiment, the anisotropically patterned alignment layer iscapable of light management property, light scattering effect or lightdiffraction.

In one embodiment, the first and second directions are perpendicular toeach other.

In one embodiment, the first surface is flexible. In one embodiment, thefirst surface is rigid.

In one embodiment, a method is described where a first surface isprovided. Laser energy is applied to the first surface to form a firstanisotropically patterned alignment layer comprimising a firstanisotropic pattern with features with a size of 0.1 nm to 500 μm. Thefirst anisotropic pattern has a first periodicity of 5 nm to 500 μm in afirst direction in the plane of the first surface. In one embodiment,the first anisotropically patterned alignment layer has features with asize of 5 nm to 500 μm.

In one embodiment, the laser energy is applied in pulses.

In one embodiment, the first anisotropic pattern has a secondperiodicity of 5 nm to 500 μm in a second direction in the plane of thesurface. The first and second directions are different and the first andsecond periodicities are different. In one embodiment, the first andsecond directions are perpendicular to each other.

In one embodiment, the first surface is a first surface of a substrate.In one embodiment, the first surface is a first surface of an electrode.

In one embodiment, the first surface is a first surface of a separatelayer disposed on an electrode or a substrate.

In one embodiment, the method further comprises providing a firstsubstrate and providing a first electrode disposed over the firstsubstrate. The first surface is disposed over the first electrode. Themethod further comprises providing a liquid crystal layer disposed overthe first surface, providing a second surface disposed over the liquidcrystal layer, providing a second electrode disposed over the secondsurface, and providing a second substrate disposed over the secondelectrode.

In one embodiment, the step of disposing a second surface comprisesapplying laser energy to the second surface to form a secondanisotropically patterned alignment layer comprising a secondanisotropic pattern with features with a size of 0.1 nm to 500 μm. Thesecond anisotropic pattern has a third periodicity of 5 nm to 500 μm ina third direction in the plane of the second surface.

In one embodiment, applying laser energy to the first surface comprisestranslational movement of the laser over the first surface in the firstdirection or, translational movement of the first surface in the firstdirection.

In one embodiment, the first surface comprises polymers. In oneembodiment, the first surface comprises inorganic materials. In oneembodiment, the first surface comprises nanoparticles of metals or metaloxides. In one embodiment, the first surface comprises carbon nanotubes.

In one embodiment, the anisotropically patterned alignment layer iscapable of generating noticeable alignment in a nematic, cholesteric,smectic, discotic, or blue phase liquid crystal layer. In oneembodiment, the anisotropically patterned alignment layer is capable ofgenerating alignment with an orientational order parameter of at leastS=0.40 in a nematic liquid crystal layer.

In one embodiment, the anisotropically patterned alignment layer iscapable of light management property, light scattering effect, or lightdiffraction.

In one embodiment, the first surface is flexible. In one embodiment, thefirst surface is rigid.

In one embodiment, the method includes applying laser energy to thefirst anisotropically patterned alignment layer to form a secondanisotropic pattern.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

FIGS. 1A-B show exemplary anisotropically patterned alignment layerswith anisotropic patterns having one periodicity.

FIG. 2 shows an exemplary anisotropically patterned alignment layer withan anisotropic pattern having two periodicities.

FIG. 3 shows FIG. 2 shows an exemplary anisotropically patternedalignment layer with an anisotropic pattern having two periodicities innon-perpendicular directions.

FIG. 4 shows exemplary cross-sectional views of anisotropicallypatterned alignment layers comprising the anisotropic patterns.

FIGS. 5A-5C show exemplary locations of the alignment layer in anelectro-optical device.

FIG. 6 shows an exemplary method of making the anisotropically patternedalignment layer using inkjet printing.

FIG. 7A shows exemplary anisotropic patterns made by inkjet printingaccording to one embodiment.

FIG. 7B shows exemplary anisotropically patterned alignment layersformed by solidification.

FIG. 8 shows wavelengths of commercially available lasers.

FIG. 9 shows exemplary anisotropically patterned alignment layers withanisotropic patterns formed by laser action according to one embodiment.

FIG. 10A-10C illustrates an example of an anisotropically patternedalignment layer made with 1064 nm laser beam at a scanning speed of 400mm/s and 20 kHz in ITO first surface. FIG. 10A shows a top view, FIG.10B shows an oblique view, and FIG. 10C shows a cross-section view.

FIG. 11 shows polarized absorption spectra of 7-micron-thick nematicliquid crystal layer used with the alignment layer of FIGS. 10A-10C.

FIGS. 12A-B show surface arrangements of nanoparticles and carbonnanotubes in the anisotropic patterns.

DETAILED DESCRIPTION OF THE INVENTION

The field-free LC orientation is provided by the boundary conditions ofa geometry confining the LC layer. These boundary conditions aredictated by the alignment layers. The basis for the molecularorientation of the LC material is the physical and/or chemicalanisotropy on the surface of an alignment film. These surfacecharacteristics result in an anisotropic arrangement of the adjacent LCmolecules.

Conventionally, the alignment layer is created by the unidirectionalmechanical rubbing of polymer films with a rubbing cloth. This methodhas been widely used due to its simplicity, durability and low-cost.However, the generation of dust and electrostatic surface charge duringthe rubbing, as well as mechanical surface defects can be detrimentalfor electro-optical device performance and lifetime. Moreover, thedebris generation is not in line with the clean-room requirements, whilethe high processing temperature of polyimide alignment films limitstheir application on many flexible substrates. Additionally, with therubbing method it is difficult to achieve different LC orientationswithin a micron-size (or smaller) domains.

To overcome the limitations of mechanical rubbing, alternative methodsfor generation of surface anisotropy may be used. One promisingalternative is photoalignment, which utilizes polarized light togenerate chemical anisotropy on photo-reactive surfaces via directionalphoto-reaction (e.g. isomerisation, anistropic cross-linking, ordirectional photo-degradation). Anisotropic intermolecular interactionsbetween different surface molecular species have been shown to besufficient to align the LC molecules. Photoalignment offers thepossibility of micro- patterning via photo-mask for multi-domain LCorientations, as well as feasibility on flexible substrates. However,the majority of the photoalignment materials suffer from long-termstability (light, thermal and/or chemical instability).

Therefore, there is a need of inexpensive LC alignment films, whichprovides stable LC of entation, with high fabrication reproducibilityand reliable continuous control. The main requirements for the alignmentlayer are its thermal- and photo-stability over time and during deviceoperation, as well as its “electrical” stability to survive many dynamic(switching) cycles under externally applied fields.

Embodiments disclosed herein relates to layers with ano-andmicro-patterned topographies made by laser action or inkjet printing fortheir potential application as alignment layers of liquid-crystallinemolecules in variety of passive and active LC-based devices, viz.light-management films, compensation films, polarizers, tunablewave-plates, variable filters, different liquid crystal display (LCD)modes (e.g. twisted nematic (TN), super-twisted nematic (STN),electrically controlled birefringence (ECB), optically compensated bend(OCB), vertical alignment (VA), dynamic ophthalmic products, tunablebeam splitters, polarized organic emitting diodes (OLEDs), bipolarorganic field-effect transistors (OFETs), etc.

Embodiments herein cover a variety of anisotropic surfacenano-/micro-topographies, which differ in their chemical nature, patternshape, size, periodicity, and anchoring strength. The nanometer- andmicrometer-size surface features of the alignment layers can provide avariety of liquid crystal (LC) orientations, including planar, tilted orhomeotropic. These alignment layers have a wide spectrum of designednano-/micro-topographies and can also provide orientation of differentrod-like and discotic-shaped LC molecules, including but not limited tonematic, smectic, cholesteric, discotic, and blue-phase LCs.

The surface topography of the alignment film and the confinement effectsof nano- and micro-structures on the overlaying LC molecules, coupledwith the complex interplay of intermolecular interactions on LC-solidsurface interface (mainly dipolar, Van der Waals, and stericinteractions), dictate the LC alignment and electro-optical(magneto-optical) response of final LC devices. Moreover, not only thephysics, but the chemistry of alignment surfaces can be tailored, whichdirectly affect the surface anchoring of LC molecules. In this way,alignment layers with tailored anchoring energy, i.e. layers that couldprovide mono-stable, bi-stable or multi-stable anchoring conditions arepossible.

The alignment layers disclosed herein, which provide the LC orientationin the field-free state of device operation, are layers with nanometer-and micrometer- size topographic features. In an electro-optical device,these alignment layers are usually located on the inner side of bothsubstrates, adjacent to the LC layer. “Alignment layer” as used hereinincludes a separate layer disposed over the substrate, a separate layerdisposed over an electrode, and the substrate or electrode acting as the“alignment layer”. Additionally, the alignment layer can be located withintervening layers between it and the LC layer. A broad spectrum ofsurface topographies can be achieved to provide specific LCorientations, ranging from no-tilt in-plane (planar) LC orientation viavariety of predetermined tilt-angle LC orientations to fully vertical(homeotropic) LC orientation.

FIG. 1 A shows an exemplary alignment layer comprised of a first surface100. The first surface has an anisotropic pattern 300 with nano ormicro-structured topographies. The nano or micro-structured topographiescan also be called surface features.

The anisotropic pattern 300 has a first periodicity 301. Preferredranges for the first periodicity include 0.1 nm to 500 μm, 0.1 nm to 1nm, 0.5 nm to 1 nm, 0.5 nm to 500 μm, 50 nm to 500 μm, and morepreferably from 5 nm to 500 μm. Generally for periodicities anddimiensions discussed throughout, smaller values may have a strongeralignment effect. Larger values may be simpler to fabricate.

The first periodicity rans in the first direction 101 of the surface100. As used herein “periodicity” is defined as the center-to-centerdistance between two neighboring surface features. This can also becalled the pitch. FIG. 1B shows another embodiment of the anisotropicpattern 300. The anisotropic pattern 300 in FIGS. 1A and 1B do not havea second periodicity in a second direction 102 of the surface.

FIG. 2 shows another embodiment of an alignment layer on a first surface100. This alignment layer is similar to the alignment layers of FIGS. 1Aand 1B except that its anisotropic pattern 300 has a second periodicity302 running in the second direction 102 of the first surface 100.Preferred ranges for the second periodicity include 0.1 nm to 500 μm,0.1 nm to 1 nm, 0.5 nm to 1 nm, 0.5 nm to 500 μm, 50 nm to 500 μm, andmore preferably from 5 nm to 500 μm. It is preferably different from thefirst periodicity 301. As shown in FIG. 2, the two directions 101 and102 that the two periodicities run in are also different from eachother. These two directions can be perpendicular to each other, like inFIG. 2, or can be at any angle to each other, like in FIG. 3

The surface features or topographies of the anisotropic pattern have asize from 0.1 nm to 500 μm. As used herein, “size” can include theheight, width, and length of the features. A surface feature preferablyhas all three dimensions (height, width, length) in that range.Alternatively, a surface feature may have only one or two dimensions inthe size range. For example, a topography of grooves may have a lengthcorresponding to a substrate dimension that exceeds the range, butgroove widths and heights within the range. The surface featuresdescribed herein can be raised or lowered from the first surface.“Height” as used herein means the distance from the first surface to thepeak of surface feature or the distance from the first surface to thevalley of the surface feature. FIG. 4 is a cross-sectional view ofexemplary alignment films, showing the height and width (dimensions d₁and d₃) of the topographies of exemplary patterns. FIG. 4 also shows d₂,the space between the end of one feature to the beginning of anotherfeature. d₂ can be from 0 to 500 μm. A zero value for d₂ means that thesurface features may touch or overlap each other but, as shown in FIG. 3a-c, there may be some periodic variation even in a direction wheresurface features touch. FIG. 4 also shows the periodicity 301 in onedirection of the first surface 100. While FIG. 4 shows topographies withcertain shapes, the embodiments disclosed herein are not limited tothose shapes and can include others known in the art. One pattern 300can have topographies of multiple shapes. Additionally, while FIGS. 1-4show the first surface having only one pattern 300, the first surfacecan contain more than one pattern in different regions of the firstsurface.

The alignment layers in FIGS. 1-4 may be incorporated intoelectro-optical devices. The alignment layer affects the alignment ofthe LC material during the field-free state. As shown in FIG. 5A, thealignment layer disclosed herein may be a surface of a substrate 400 inan electro-optical device. In other embodiments, it may be a surface ofan electrode 500 as shown in FIG. 5B. In other embodiments still, it maybe a separate alignment layer 600 that is disposed over an electrode orsubstrate layer in the device as shown in FIG. 5C. An electro-opticaldevice may have one or more alignment layers. Preferably, there are twoalignment layers, placed adjacent to the liquid crystal layer. This isshown in FIG. 5C with alignment layers 500 and 800. However, thealignment layer can be placed such that there are intervening layersbetween the LC layer and the alignment layer.

The alignment layers disclosed herein are capable of generatingnoticeable alignment in a LC layer. These LC layers include but are notlimited to nematic, cholesteric, smectic, discotic, and blue-phaselayers. As used herein, “noticeable alignment” means an orientationalorder parameter S in the LC molecules greater than the absolute value of0.3, and preferably greater than the absolute value of 0.4. Preferably,these alignment layers are capable of generating alignment with anorientational order parameter of at least 0.50 in a nematic liquidcrystal later.

The alignment layers disclosed herein can be rigid or flexible,depending on the characteristic of the first surface.

In some embodiments, the alignment layers disclosed herein and theirnano- and micro-structured topographies can be made by inkjet printing.In other embodiments, they can be made by laser action. These methodsare described below.

Inkjet printing is a solution dispensing technique that is characterizedby its non-contact and material-efficient processing in ahighly-reproducible manner.

The final surface features of the alignment layers made by inkjetprinting are highly dependent on the processing parameters. Theseparameters include but are not limited to the inkjet nozzle diameter,the volume of the droplets, the temperatures of the solution andsubstrate, the moving speed of substrate (or inkjet), and materialproperties of the substrate and the solution. The material propertiesinclude but are not limited to: the nature of the solution used,specifically the solvent used and its viscosity, vapor pressure andsurface tension; ink or solution concentration; and the nature of thesubstrate (for example, its wetting characteristics). Overall, the finaltopography is a complex interplay of many factors. One of skill in theart, with the benefit of this disclosure, can readily use theseparameters to generate disclosed surface features.

In one embodiment, the alignment layer is made by depositing a solution200 over the first surface 100. The first surface can be the firstsurface of a substrate, electrode, or a separate layer disposed on anelectrode or a substrate. In some embodiments, the solution is ink. Asseen in FIG. 6, depositing can be done in some embodiments by ejectingink droplets 201 from an inkjet printing nozzle 3000 in a drop-by-dropmanner. The nozzle diameter has an effect on the droplet size. Whendepositing is ejecting ink droplets, the nozzle diameter of the inkjet,together with the volume of the ejected droplets and their subsequentcoalescence on the substrate surface, will partially define the finalsurface features that form. In one embodiment, the nozzle diameter is 50nm to 500 μm, preferably from 50 nm to 1 μm. However, one of ordinaryskill in the art, with the benefit of this disclosure, can readilygenerate the disclosed surface features with any suitable nozzlediameter.

The solution is deposited on the first surface 100 such that ananisotropic pattern 1600 is formed on the first surface 100. The dotspacing (defined as the center-to-center distance between twoneighboring droplets of solution) and the rate of substrate-/inkjetprinting nozzle-movement, will affect the anisotropic pattern that isformed and the periodicities present in the anisotropic pattern. In someembodiments, the nozzle is moved while the first surface is kept still.In other embodiments, the first surface 100 is moved.

FIGS. 7 a-7 c show exemplary resulting anisotropic patterns. As seen inFIGS. 7 a-c, each anisotropic pattern 1600 created by the depositedsolution has a periodicity 301 in the first direction 101 of the firstsurface and a second periodicity 302 in a second direction 102 of thefirst surface 100. Preferred ranges for the first and secondperiodicities include 0.1 nm to 500 μm, 0.1 nm to 1 nm, 0.5 nm to 1 nm,0.5 nm to 500 μm, 50 nm to 500 μm, and more preferably from 5 nm to 500μm. The initial anisotropic pattern 1600 has an effect on the resultinganisotropically patterned alignment layer. Thus, an anisotropic pattern1600 having two periodicities may have different periodicities, with onebeing bigger than the other. In this way, after solidification of theanisotropic pattern 1600, directional channels/grooves are formed in thefirst surface 100 such that it can be used as an alignment layer. Thedirections 101 and 102 can be parallel to the first surface's x axis andy axis or in other directions as long as they are different from eachother. In some embodiments, the directions 101 and 102 may beperpendicular to each other. While not shown, embodiments herein alsoinclude anisotropic patterns 1600 that have only one periodicity 301 inone direction 101.

After depositing the anisotropic pattern 1600, the solution issolidified in order to from an anisotropically patterned alignment layerwith anisotropic pattern 300. Anisotropic pattern 300 here is similarwith similar attributes of those described in FIGS. 1-4. The surfacefeatures may have a size from 0.1 nm to 500 μm. Smaller ranges may bebetter for LC alignment, thus, the size is preferably from 0.1 nm to 1nm, 0.5 nm to 1 nm, 0.5 nm to 500 μm, 5 nm to 500 μm, and morepreferably from 50 nm to 500 μm. As used herein “solidifying” or“solidified” includes any method that turns the solution into a solid,including cross-linking, solvent evaporation, a combination of the two,or other methods known in the art.

In one embodiment, the step of solidifying may alter anisotropic pattern1600 such that the resulting anisotropic pattern 300 on theanisotropically patterned alignment layer is different from the initialanisotropic pattern 1600. For example, in some embodiments, the solution200 may have viscosity or surface tension properties that cause thesolution to coalescence during solidification. Additionally, the firstsurface 100 may have surface wetting characteristics that contribute tothe coalescence of the solution 200. FIG. 8 a-8 c show exemplarytopographies after the solution is solidified on the first surface.These topographies show a coalescence of the deposited solution. Thefinal anisotropic patterns 300 shown in FIG. 8 a-8 c are different fromthe deposited patterns 1600 shown in FIGS. 7 a-7 c. The solutionviscosity, density and concentration, the ink and substrate temperature,as well as the nature of the solvent(s) used, especially solvent vaporpressure and evaporation rate will determine the final pattern on thefirst surface. Additionally, some solutions might require additionalbaking by UV irradiation or by IR heating during solidification, atwhich stage the solution shrinkage will play a major role in the finalshape of the anisotropic pattern 300.

In some embodiments, the anisotropic pattern 300 is solidified in such amanner that the deposited anisotropic pattern 1600 is the same as finalanisotropic pattern 300 on the anisotropically patterned alignmentlayer. For example, in some embodiments, the solution and the substrateproperties are not conducive to coalescence and the drops do notcoalescence. As used herein, “change” or “different” includes a changein the size and shape of the pattern's features. Despite the amount ofcoalescence or change between the two patterns 1600 and 300, theresulting anisotropic pattern 300 still retains at least some structureof the periodicities contained in the anisotropic pattern 1600.

In some embodiments, the pattern's chemical nature may also affect theorientation of overlaying LC molecules. Thus, the type of solution usedin the method not only affects the final pattern, but will also affectthe orientation of the LC molecules due to its chemical interaction ofthe pattern with the molecules of the LC layer. For example, a patternmade of solution comprising acrylate may generate very different LCorientations than the same pattern made from a solution comprisingTeflon. In the case of acrylate patterns, the LC alignment is mostlikely to be planar or low tilt planar LC alignment, while Teflonpatterns are expected to cause a homeotropic LC alignment. Solutionsused in the method disclosed herein include but are not limited to thosecomprising solvents, surfactants, and binders such as conjugatedpolymers, acrylates, urethanes, organosilanes, epoxies, alcohols,ketones, aldehydes, alkanes, alkenes, or chlorinated solvents.

In some embodiments, solutions used to deposit patterns may includenanoparticles of metals, metal oxides, and/or carbon nanotubes,individually or in any combination. Such nanoparticles/nanotubes mightfurther help in the orientation of the overlaying LC molecules, but alsomight contribute to additional property of the alignment layer such aslight diffraction, light management (including but not limited tofocusing or defocusing light rays), or light scattering effects. Byadjusting the inkjet printing conditions and their coalescent behavior,the nanoparticles/nanotubes might be “ordered” in certain patterns onthe substrate surface. This ordering is shown in FIGS. 12A-B. Thealignment layers made by this method thus results in the anisotropicallypatterned alignment layers as described in FIGS. 1-4.

In some embodiments, methods may further include steps for incorporatingthe first surface 100 into an electro-optical device as shown in FIG.5C. These steps comprise providing a first substrate 400 and providing afirst electrode 500 disposed over the first substrate. The method mayfurther comprise disposing the first surface 100 over the firstelectrode 500, providing a liquid crystal layer 700 disposed over thefirst surface, providing a second surface 1100 disposed over the liquidcrystal layer, providing a second electrode 900 disposed over the secondsurface, and providing a second substrate 1000 disposed over the secondelectrode 900. As used herein, “disposed over” allows for interveninglayers between the first surface and the substrate. The second surface1100 has a second anisotropic pattern 1300 formed on the second surface.The second anisotropic pattern 1300 is similar to the anisotropicpattern 300 and is formed in the same manner as the first anisotropicpattern 300.

In one embodiment, the alignment layers described in FIGS. 1-4 may bemade by laser action. The resulting surface features described in FIGS.1-4 may be highly dependent on the first surface material properties, aswell as the laser processing parameters (for example including but notlimited to laser pulse, laser power, and laser scanning rate). Overall,the final topography of the alignment layer is a complex interplay ofmany factors including but not limited to material properties and laserparameters. One of skill in the art, with the benefit of thisdisclosure, can readily use these parameters to generate disclosedsurface features.

In some embodiments, to make the anisotropically patterned alignmentlayer in FIGS. 1-4, laser energy is applied to a first surface 100 toform a first anisotropic pattern 300 with surface features. Thesefeatures have sizes from 0.1 nm to 500 μm. Smaller ranges may be betterfor LC alignment, thus, the size is preferably from 0.1 nm to 1 nm, 0.5nm to 1 nm, 0.5 nm to 500 μm, 50 nm to 500 μm, and more preferably from5 nm to 500 μm. The features may have at least one of length and widthin the range from 0.1 nm to 50 nm, preferably 0.5 nm to 50 nm.

The first surface can be a surface on a substrate, a surface on anelectrode, or a surface of a separate layer.

The laser pulse and the rate of laser beam and/or alignment layertranslational movement, may affect the surface patterns. The laserenergy is applied to the first surface in such a manner that the spaceto space distance between two adjacent pulses (herein called “laserpulse spacing”). Preferred ranges for the laser pulse spacing include0.1 nm to 500 μm, 0.1 nm to 1 nm, 5 nm to 1 nm, 0.5 nm to 500 μm, 50 nmto 500 μm, and more preferably from 5 nm to 500 μm. Thus, the resultingalignment layer has an anisotropic pattern 300 with a first periodicity301 in a first direction 101 in the plane of the surface. This is shownin FIG. 9.

The laser energy can also be applied in a manner such that theanisotropic pattern 300 has a second periodicity 302 in a seconddirection 102. Preferred ranges for the second periodicity include 0.1nm to 500 μm, 0.1 nm to 1 nm5 nm to 1 nm, 0.5 nm to 500 μm, 50 nm to 500μm, and more preferably from 5 nm to 500 μm. FIG. 9 is a schematicpresentation of different anisotropic pattern 300 formed in firstsurfaces 100. Some of these patterns have two periodicities 301 and 302running in two different directions 101 and 102 in the plane of thefirst surface 100. While they are shown running in the x-y axis of thefirst surface, they can run in different directions not aligning withthe x-y axis of the first surface. Additionally, the directions can benon-perpendicular to each other. These periodicities in conjunction withthe first surface's reaction with the laser energy will define the finalanisotropic patterns 300 in the first surface. For the purpose ofcreating the alignment layers disclosed in FIGS. 1-4, the firstperiodicity 301 is different from the second periodicity 302. In thisway, directional channels/grooves are formed in the first surface 100.Embodiments, herein, however, also include alignment layers with ananisotropic pattern 300 with only one periodicity running in onedirection of the first surface. FIG. 9 shows both types of anisotropicpatterns 300.

Embodiments disclosed herein may be implemented with any commerciallyavailable laser or other suitable laser, and can be of different nature,gas lasers, liquid lasers, or solid state lasers of differentwavelengths, depending on the material of the first surface. Theseinclude but are not limited to ND: ASE, Ar-Laser, CO₂-laser. The laseraction with the first surface material can be of different nature,including but not limited to melting the material, burning/evaporatingthe material, curing the material, and etching the material. FIG. 8gives an overview of different commercially-available lasers (includingtheir operational wavelengths) with continuous and pulsed emission.Laser types with distinct laser lines are shown above the wavelengthbar, while below are shown lasers that can emit in a wavelength range.The height of the lines and bars gives an indication of the maximalpower/pulse energy commercially available, while the color codifies thelaser material. Most of the data comes from Weber's book Handbook ofLaser Wavelengths.

In some embodiments, the anisotropic pattern's chemical nature maygreatly affect the orientation of overlaying LC molecules on suchpatterned surfaces. The pattern's chemical nature is affected by thecomposition of the first surface. Thus, the first surface 100 on whichthe laser energy is applied may be comprised of inorganic materials,including but not limited to ITO, SIO₂, ZrO₂, and ZnO₂. For example, thesame patterns made in ITO or SiO₂ or Teflon material might generate verydifferent LC orientations. In the case of patterns made in a firstsurface comprising ITO, the LC alignment is most likely to be planar orlow-pretilt planar LC alignment, while a homeotropic LC alignment isexpected on the same patterns made in a first surface comprisingTeflon-like material. For example, in one embodiment, the laser beamwith wavelength of 1064 nm is applied over a first surface comprised ofITO or SIO₂, generating surface patterns by directional materialremoval, i.e. material etching.

In some embodiments, the first surface may be comprised of polymers. Forexample, in one embodiment, the laser beam with wavelength of 365 nm isscanned over a first surface comprised of acrylate prepolymer(exhibiting a significant degree of shrinkage upon cross linking),generating directional surface features by anisotropiccross-linking/shrinkage/wrinkles (i.e. directional curing of thematerial). Moreover, the laser beam can be linearly-polarized generatinga wider spectrum of directional features in the “directionally-reactive”first surface material. In another embodiment yet, a powerful laser canbe used to create anisotropic patterns 300 by burning/evaporation of thematerial of the first surface. Theoretically, the inkjet method can beapplied to surface/substrate made of any material. Depending on theinteraction of the solution and the substrate material, a variety ofsurface features are possible. In the laser method, substrate materialshave certain types of interaction with the laser beam. For example, apolyacrylate substrate or polycarbonate substrate may not interactsignificantly with a laser beam of 1064 nm, but these two substrates canbe used with the inkjet printing method. There will be materialsapplicable for both types of methods, inkjet and laser, for example,metallic/conductive surfaces. However, the resulting patterns on thesame substrate material made with the two methods can be different, andconsequently, can give different LC alignments, i.e. differentorientational order parameters.

In some embodiments, the laser can be continuous or pulsed laser. In thecase of continuous laser, various scanning speeds of the laser beam overthe first surface, or various translational movements of the firstsurface under the static laser beam, or various mutual translationalmovements of both, the laser beam and the first surface, are possible.In the case of pulsed laser, the laser intensity (the pulseintensity/power), the pulse frequency and laser scanning speed can bevaried in a manner to generate the desirable anisotropic pattern 300.Also, in the case of pulsed laser, translational movement of the laser,first surface, or both are possible.

In some embodiments, the first surface 100 may further comprisenanoparticles of metals or metal oxides, and carbon nanotubes,individually or in any combination. The laser might have differentinteractions with the nanoparticles/nanotubes than with the surroundingmaterial/matrix. By adjusting the laser processing conditions, a varietyof patterns are possible in first surface materials containingnanoparticles/nanotubes as shown in FIGS. 12A-B. Suchnanoparticles/nanotubes might further help in the orientation of theoverlaying LC molecules, but also might contribute to an additionalproperty of the alignment layer, such as light diffraction properties,light management property (including but not limited to focusing ordefocusing light rays) and light scattering effects.

The method may further include steps for incorporating the first surface100 into an electro-optical device as shown in FIG. 5C. These stepscomprise providing a first substrate 400 and providing a first electrode500 disposed over the first substrate. The method can comprise disposingthe first surface 100 over the first electrode 500, providing a liquidcrystal layer 700 disposed over the first surface, providing a secondsurface 1100 disposed over the liquid crystal layer, providing a secondelectrode 900 disposed over the second surface, and providing a secondsubstrate 1000 disposed over the second electrode 900. As used herein,“disposed over” allows for intervening layers between the first surfaceand the substrate. The second surface 1100 has a second anisotropicpattern 1300 formed on the second surface. The second anisotropicpattern 1300 is similar to the anisotropic pattern 300 and is formed inthe same manner as the first anisotropic pattern 300.

Modeling

By way of non-limiting example, FIG. 10A-C show surface patterns made inITO layer with 1064 nm laser beam at scanning rate of 400 mm/s andfrequency of 20 kHz. As seen in FIGS. 10A-C, there is good patternreproducibility. Groove depths of about 20 nm were achieved by laseretching action in the ITO layer. The resulting alignment layer has a 70μm periodicity in the horizontal direction of the first surface. Thelaser pulses were sufficiently close together that the grooves do notshow noticeable periodicity in the scanning direction.

The surface pattern shown in FIGS. 10A-C was further tested for its LCalignment capability. For this purpose, 7-micron-thick nematic LC celllightly doped with a dichroic dye (Disperse Red 1) was prepared.Commercially-available nematic LC MDA-98-1602 (Merck) was doped with0.3-0.5 wt % dichroic dye Disperse Red 1 (Sigma Aldrich), and then,injected in an empty LC cell, previously prepared with substrates thathave ITO layers with patterns made by laser etching (like those in FIG.4). The empty LC cell was filled with the dye-doped nematic LC attemperature above the clearing temperature of the LC crystal, and then,it was cooled down slowly to room temperature. To assess the quality ofLC alignment, a dye polarized absorbance was recorded for this cellunder the assumption that the dichroic dye (Disperse Red 1) is orientedit the same manner as the surrounding rod-like LC molecules. In FIG. 11below, the polarized absorption spectra of the dye doped in the nematicLC. Due to the orientation of the dye within the nematic host, adifference in the dye polarized spectra A_(parallel) andA_(perpendicular) (A_(parallel)=dye absorbance parallel to the alignmentdirection; A_(perpendicular)=dye absorbance perpendicular to thealignment direction) was observed. Furthermore, the orientational orderparameter, S, was calculated for this cell according to the followingequations:

$\begin{matrix}{R = \frac{A_{parallel}}{A_{perpendicular}}} \\{S = \frac{R - 1}{R + 2}}\end{matrix}$

where R is the dichroic ratio, A_(parallells) the dye absorbanceparallel to the alignment direction and A_(perpendicular) is the dyeabsorbance perpendicular to the alignment direction. The alignment layerachieved very good LC alignment expressed with a high orientationalorder parameter S of 0.55.

1. A method comprising: providing a first surface; depositing a solutionover the first surface via inkjet printing to form a first anisotropicpattern; and solidifying the solution to form a first anisotropicallypatterned alignment layer having features with a size of 5 nm to 500 μm;wherein: the first anisotropic pattern formed by the deposition has afirst periodicity of 5 nm to 500 μm in a first direction in the plane ofthe first surface.
 2. A method of claim 1, wherein the first anisotropicpattern formed by the deposition has a second periodicity in a seconddirection in the plane of the surface; wherein: the first and seconddirections are different; the first and second periodicities aredifferent; and the second periodicity is 5 nm to 500 μm.
 3. The methodof claim 1, wherein depositing a solution includes depositing drops ofthe solution; and solidifying the solution includes a partialcoalescence of the drops while retaining at least some structure of thefirst periodicity.
 4. The method of claim 1, wherein the first surfaceis a first surface of a substrate.
 5. The method of claim 1, wherein thefirst surface is a first surface of an electrode.
 6. The method of claim1, wherein the first surface is a first surface of a separate layerdisposed on an electrode or a substrate.
 7. The method of claim 1,further comprising: providing a first substrate; providing a firstelectrode disposed over the first substrate; disposing the first surfaceover the electrode; providing a liquid crystal layer disposed over thefirst surface; providing a second surface disposed over the liquidcrystal layer; providing a second electrode disposed over the secondsurface; providing a second substrate disposed over the secondelectrode.
 8. The method of claim 7, wherein providing a second surfacecomprises: depositing a solution over the second surface via inkjetprinting to form a second anisotropic pattern; and solidifying thesolution to form a second anisotropically patterned alignment layerhaving features with a size of 5 nm to 500 μm; wherein: the secondanisotropic pattern formed by the deposition has a third periodicity of5 nm to 500 μm in a third direction in the plane of the second surface.9. The method of claim 8, wherein the second anisotropic pattern has afourth periodicity in a fourth direction in the plane of the secondsurface; wherein: the third and fourth directions are different; thethird and fourth periodicities are different; and the fourth periodicityis 5 nm to 500 μm.
 10. (canceled)
 11. The method of claim 1, wherein thestep of solidifying the solution comprises shrinking the solutionthrough ultra-violet irradiation.
 12. The method of claim 1, wherein thestep of solidifying the solution comprises shrinking the solutionthrough infra-red heating.
 13. The method of claim 1, wherein thesolution comprises one of or a combination of conjugated polymers,acrylates, urethanes, organosilanes, and epoxies.
 14. The method ofclaim 1, wherein the solution comprises surfactants or binders.
 15. Themethod of claim 1, wherein the solution comprises a solvent comprisingone or a combination of alcohols, ketones, aldehydes, alkanes, alkenes,or chlorinated solvents,
 16. The method of claim 1, wherein the solutioncomprises nanoparticles of metals or metal oxides.
 17. The method ofclaim 1, wherein the solution comprises carbon nanotubes.
 18. The methodof claim 1, wherein the anisotropically patterned alignment layer iscapable of generating noticeable alignment in a nematic, cholesteric,smectic, discotic, or blue-phase liquid crystal layer.
 19. The method ofclaim 1, wherein the anisotropically patterned alignment layer iscapable of generating alignment with an orientational order parameter ofat least S=0.50 in a nematic liquid crystal layer.
 20. The method ofclaim 1, wherein the anisotropically patterned alignment layer iscapable of light management property, light scattering effect, or lightdiffraction. 21-25. (canceled)
 26. A method comprising: providing afirst surface; and applying laser energy to the first surface to form afirst anisotropically patterned alignment layer comprising a firstanisotropic pattern with features with a size of 0.1 nm to 500 μm;wherein the first anisotropic pattern has a first periodicity of 5 nm to500 μm in a first direction in the plane of the first surface. 27-46.(canceled)